Over the years, the Marvel Cinematic Universe has taken audiences to some fantastic places. After Phase 1, the MCU left Earth more and more as it expanded to include characters such as the Guardians of the Galaxy and Thanos. Eventually, the cinematic universe grew to include no less than 28 different planets, including Earth.
Two scientists, Simon Clark and Dr. Hannah Wakeford, went through every film in the "Infinity Saga" and examined each planet. Using their combined knowledge of physics and planetary science, Clark and Wakeford were able to look at and explain the plausibility of visually unique planets such as the garbage planet of Sakaar, the dark planet of Vormir and the flat, disc-like world that was Asgard. They concluded that out of the 28 planets introduced thus far, just 19 would be able to physically exist in the real world. Of the impossible planets were Asgard, Sovereign and Vormir, among others, for a number of complex reasons.
Phase 4 will likely see the introduction of even more unique worlds with films such as The Eternals and Doctor Strange and the Multiverse of Madness, both of which seem to focus on settings beyond Earth. In fact, Marvel Studios President Kevin Feige has made clear in the past that the next phase of the MCU will focus on cosmic elements, so there's likely to be a lot more in the pipeline.